1. Field of the Invention
The present invention relates to a receiving technology and, more particularly, to a receiving method and apparatus receiving a signal in which a plurality of carriers are used.
2. Description of the Related Art
The orthogonal frequency division multiplexing (OFDM) modulation scheme is known as a communication scheme which is robust in a multipath environment, while enabling high-speed data transmission. The OFDM modulation scheme is used in IEEE802.11a, IEEE802.11g and HIPERLAN/2, which are available as wireless LAN standards. In wireless LAN, a signal is received over a transmission channel environment with time-dependent variation. Frequency-selective fading also affects the signal. Therefore, a receiving apparatus performs dynamic channel estimation. For channel estimation in a receiving apparatus, two types of known signals are provided. One is a known signal provided at the head of a burst signal for the entire set of carriers. This type of signal is referred to as a preamble or a training signal. The other is provided for a selected carrier in the middle of data block of the burst signal. This type of signal is referred to as a pilot signal (See reference (1) in the following Related Art List, for instance).
Related Art List
(1) Sinem Coleri, Mustafa Ergen, Anuj Puri, and Ahmad Bahai, “Channel Estimation Techniques Based on Pilot Arrangement in OFDM Systems”, IEEE Transactions on broadcasting, 48, No. 3, vol. pp. 223-229, September 2002.
A receiving apparatus subjects a received signal to Fourier transform so as to filter out signals in individual carrier channels (hereinafter, referred to as subcarrier signals). The receiving apparatus further conducts channel estimation adapted for the individual carriers. The receiving apparatus demodulates the received signal by dividing the signal in each of the carrier channels by the transmission channel property estimated for the carrier. A system known as a Ultra Wide Band (UWB) system is being developed as a system delivering a higher data transmission rate than wireless LAN described above. In the UWB system, a data transmission rate ten times higher than that of wireless LAN is delivered. In a situation where the OFDM modulation scheme is applied to the UWB system, multipath effects become more serious as the data transmission rate is increased. In a quadrature modulation scheme such as 16 QAM, this might lead to significant degradation in characteristics due to multipath.
For this reason, the use of QPSK, characterized by the highest transmission quality of the various modulation schemes used in wireless LAN, is suitable. In order to enable a data transmission rate of approximately 10 times higher than wireless LAN using QPSK as a modulation scheme, however, the transmitting apparatus and the receiving apparatus are required of an operation at a higher operating clock than that of wireless LAN. As the operating clock becomes higher, there is an associated increase in power consumption. In particular, the receiving apparatus generally processes a larger number of data bits than the transmitting apparatus and performs more complex processes. Therefore, power consumption in the receiving apparatus is larger. At the same time, for battery-driven operation of the receiving apparatus and the transmitting apparatus, it is preferable that power consumption be small.